Journal of Neuroscience, Vol 5, 2443-2452, Copyright © 1985 by Society for Neuroscience
The postnatal development of the association projection from visual cortical area 17 to area 18 in the cat
DJ Price and C Blakemore
The postnatal development of the association projection from area 17 to
area 18 was studied in normal and binocularly deprived kittens between 1
and 28 days of age, using retrograde transport of horseradish peroxidase
conjugated with wheat germ agglutinin. The positions of injection sites in
the visual cortex, defined in relation to the borders of visual areas 17,
18, and 19 located in Nissl- and cytochrome oxidase-stained sections, were
confirmed by observing the patterns of labeling of cells in the lateral
geniculate nucleus. The association projection is present and is arranged
at least roughly topographically from birth onward; at all ages it arises
from cells in both the superficial layers (II, III, and the upper part of
IV) and the deep layers (V and VI). In older kittens (20 days or more),
however, the origin of the pathway is principally from the upper layers, as
in adult cats, whereas in younger animals the projection arises roughly
equally from cells in superficial and deep laminae. Initially, the
association neurons in area 17 are distributed uniformly along each lamina.
Periodic clustering of labeled cells in the upper layers can just be
discerned at 10 days, and this patchiness has reached its adult clarity by
20 days, at which stage the projection from the lower layers is greatly
diminished. Binocular deprivation until the age of 28 days did not prevent
these developmental changes in the projection. Various controls established
that the patterns of labeling seen in this study were not due to direct
spread of tracer into area 17, to uptake of tracers by fibers-of-passage,
or to transcellular transport via the thalamus.